A trial of vitamin D and calcium on bone density and muscle strength at the hip in elderly women(n=336) and men(n= 140) will complete 3 years by June 1996. No blacks are in the trial. Bone density is higher in blacks which may explain their lower incidence of hip fracture but differences in other components of bone strength at the hip, including geometry, architecture and quality of bone and better muscle strength, lower incidence of falls or better absorption of the energy by soft tissues may also be involved. There are two goals: I. complete vitamin D and calcium trial at three years; II. study blacks to compare differences with whites in bone strength, fall frequency, soft tissue distribution and muscle strength at the hip and elucidate mechanisms responsible for differences. To achieve the first goal, extension of funding for the trial from Dec 1995 to June 1997 is requested. To achieve the second goal, two hypotheses will be tested: (1) the lower incidence of hip fractures in blacks is due to (a) greater bone strength at the hip which is due to higher bone density but also involves other components of bone strength, including bone architecture, geometry and quality; and (b)greater muscle mass and strength at the hip. (2) Bone density, architecture, geometry, and bone quality at the hip contribute independently, to predicting elderly black women and black and white men who have sustained a hip fracture. The first hypothesis will be tested by studying 350 black women and 150 black men over the age of 60. The variables that will be measured or recorded include: bone density, architecture, geometry and quality; mineral homeostasis and bone turnover; net calcium absorption and fractional radiocalcium absorption; frequency and type of fall; muscle strength; soft tissue distribution at the hip. The data in blacks will be compared with data already collected on white men and women. The second hypothesis will be tested by a case-control study of 50 black women, 50 black men and 50 white men who have had a hip fracture, using the 500 subjects studied in hypothesis (1) as black controls and 476 subjects in goal I. as white controls, and comparing the results in our published study of white women with hip fracture, the controls for which were also the women at base line in the trial of vitamin D and calcium. These studies will yield data on the factors related to hip fracture in blacks, and by comparing these with data already collected in whites from the same region, will allow the determinants of hip fracture in both populations to be identified.